Phase 6: fix the live Home Assistant write (Local Calendar, no event id)

The first live run against the new calendar.school entity failed loudly twice,
and both causes are fixed here.

- The Local Calendar rejects `return_response` on calendar.create_event. The
  client retries the call without it and ignores the changed-states array that
  Home Assistant returns instead.
- Home Assistant then reports no event id. The item keeps the description
  marker ([compass-nhs:<id>]) as its reference, so it leaves the candidate set
  and is never written twice. The live retry proved it: both events already in
  the calendar were adopted by their markers, with no duplicate.
- calendar.get_events reports `start` / `end` (a date-time or a bare date), not
  `start_date_time`; the reader now accepts all three shapes.

A model must no longer classify events. The calendar write depends on the
school-event rule, and the LLM labelled every event "normal"; events now keep
the deterministic rule under both classifiers.

Also fix the Phase 5 screenshot script: the calendar banner shares the `.scan`
class, so select each banner by its labelled section.

Docs record the accepted decision: Sam chose a Home Assistant Local Calendar,
so the target is calendar.school.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

README.md

@@ -15,10 +15,10 @@ re-run never duplicates an event) and it fails loudly (a failed write is shown
 on the dashboard and recorded in `calendar_pushes`). See
 [`docs/phase-6-calendar-notes.md`](docs/phase-6-calendar-notes.md).
 
-**Open decision:** the brief says *not Google*, and Home Assistant has no
-non-Google writable calendar yet. The target entity is configurable
-(`SCHOOL_HA_CALENDAR_ENTITY`) and the question is on
-[AUD-110](/AUD/issues/AUD-110).
+The target is a **Home Assistant Local Calendar**, `calendar.school` (added
+2026-10-15 after Sam chose it over the Google-backed entities that Home
+Assistant had). The entity stays configurable with
+`SCHOOL_HA_CALENDAR_ENTITY`.
 
 ```bash
 scripts/calendar-push.sh entities      # list the writable calendar entities